The invention relates to a method for controlling the lean operation of an internal combustion engine, especially an internal combustion engine of a motor vehicle, provided with a nitrogen oxide storage catalyst.
Control mechanisms in internal combustion engines for obtaining exhaust gases free to the greatest extent possible of pollutants have been disclosed; the oxygen content of the exhaust gas flow is measured and evaluated in such control mechanisms. In one generic, generally known process and a corresponding device, a special configuration is provided in the area of the exhaust catalyst, one consisting of a so-called lambda control probe upstream from the exhaust catalyst and a lambda guidance probe downstream from the exhaust catalyst. The efficiency of pollutant reduction by means of the exhaust catalyst is evaluated by means of the lambda control mechanism as a function of the probe signals determined by means of the two probes in the so-called two-point lambda control process. As soon as it is determined in the context of this evaluation that the catalyst no longer has an adequate conversion rate, a warning signal, for example, may be emitted which indicates catalyst replacement. The lambda control probe normally is a so-called constant lambda probe which can pick up a relatively wide lambda control signal in the range of approximately 0.7 to approximately 2. The lambda control probe is used to determine the lambda value of the exhaust gas composition upstream from the exhaust catalyst as a decisive influencing parameter for the conversion efficiency of an exhaust catalyst. Conversion for HC and CO, as well as for NOx, assumes very good values only over a very small lambda range of approximately 0.99 to 1.01. The lambda guidance probe is normally a binary lambda probe of very high accuracy for precise adjustment of a lambda value. Corresponding wiring is necessary for both sensors, and structural space required must be present for the two sensors.